In the past, engine-powered tools for trimming the foliage of hedges, etc., were ergonomically structured to allow angle alteration by rotating and setting the handle of the tool relative to the trimming position and the operator's stance. In addition, a structure that prevented the blade from moving was utilized in order to prevent inadvertent trimming of unintended locations when rotating the handle.
For example, Patent Literature 1 discloses art for locking the throttle lever immovable while the handle is in rotatable state. This is done by using a lever compound body connected to a protrusion that locks rotation of the handle by fitting into grooves provided in the tool body and a lever member of the throttle lever that abuts the throttle anchor lever.    Patent Literature 1: Unexamined Japanese Patent Application KOKAI Publication No. 2005-160303.